Liquid crystal display devices have been used as displays of various devices thanks to their lightness, slimness and low power consumption. In particular, active-matrix liquid crystal display devices comprising transistors arranged in respective pixels have become widespread as displays of various devices, for example, TV receivers, vehicle-mounted displays such as car navigation devices, notebook computers, tablet PCs, mobile terminals such as cellular telephones and smartphones, and the like.
Recently, research and development of thin-film transistors (TFTs) using an organic semiconductor and an oxide semiconductor, having a higher electron drift velocity than amorphous silicon TFTs used in the liquid crystal display devices have been conducted actively. In TFT using the organic semiconductor and the oxide semiconductor, a single-channel transistor (pMOS or nMOS) is used.
Incidentally, a drive circuit which drives a line group of scanning lines and the like is provided in a display area, in a liquid crystal display device. A scanning line driver composed of a single-channel transistor (for example, nMOS transistor) is well known as such a drive circuit. The scanning line driver sequentially drives the scanning lines, a video signal is written in pixels connected to the driven scanning lines, and the video is thereby displayed. The scanning line driver uses the single-channel transistor for a shift register which shifts the phase of the input signal and outputs the signal.
In contrast, a liquid crystal display device equipped with what is called an in-cell type touch detection function in which a common electrode for display originally provided in the liquid crystal display device serves as one of a pair of touch sensor electrodes while the other electrode (touch detection electrode) is disposed to cross the common electrode has been proposed.
In the liquid crystal display device equipped with what is called an in-cell type touch detection function, since the touch operation and the display operation are driven by time division, the touch operation is executed by temporarily stopping the drive of the scanning line, and then the drive for display is restarted at the scanning line position where the drive of the scanning line is stopped. In the scanning line driver composed of the single-channel transistor, the drive of the scanning line cannot be restarted by allowing a current to leak from the single-channel transistor in a period in which the drive is temporarily stopped, and the drive of the scanning line may be stopped.